Nowadays, in order to obtain high-resolution pictures having good quality using a portable terminal, particularly in a mobile phone camera, a function of precisely and rapidly controlling the focus on a desired subject at the time of taking a picture has been gradually and now widely employed. Methods adopted to automatically control the focus on a subject may include an electronic image control method and an optical control method. Such an electronic image control method is a scheme for controlling the focus using software, and has fundamental limitations in control speed or image quality.
Generally, an optical control method, which is widely used in high-end cameras, is a method of controlling the focus on a subject by mechanically moving a lens or the like, and is disadvantageous in that a micro-motor or the like is provided or in that a large number of components are required to implement a complicated mechanism, thus making it difficult to realize a small-sized camera module.
According to a conventional technology disclosed in U.S. Patent Publication No. 2006/0192885 A1 related to such an optical control method, a lens barrel is disposed on a plate connected to a spring to use a lens for a focusing device for micro-cameras, thus adjusting the motion of the lens. This invention enables the precise adjustment of the lens using a linear spring, but is problematic in that the volume of a magnet inducing a magnetic field is large and a great force is required to move the lens barrel having a predetermined weight, and thus high voltage is necessary. Further, as another related conventional technology, there is U.S. Patent Publication No. 2007/0024155 A1. According to this invention, an actuator, in which a plurality of pillars, inducing an electrostatic force when a voltage is applied, is formed on a plate and a bottom for supporting a lens and which is thus linearly movable using the electrostatic force induced by the voltage, was proposed. However, this invention is problematic in that a driving range is limited according to the number of formed pillars and the shape of electrodes.